Use of aminoimides as polyurethane catalysts

ABSTRACT

Covers a method of producing a polyurethane by utilizing aminoimide compounds as catalysts in reacting an organic polyisocyanate with an organic polyester polyol or polyether polyol in the presence of said catalyst. Said aminoimides have the formula: ##STR1## where R 1  and R 2  are independently alkyl, or when taken together are selected from the group consisting of morpholino and piperazino, R 3  is selected from the group consisting of --CH 2  CH 2  --, --CH 2  CH 2  CH 2  -- and ##STR2## AND N IS A NUMBER OF 1-6.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to the field of urethane catalysts. Moreparticularly, this invention relates to the use of certain aminoimidesas urethane catalysts.

2. Description of the Prior Art

The use of a catalyst in preparing polyurethanes by the reaction of apolyisocyanate, a polyol and perhaps other ingredients is known. Thecatalyst is employed to promote at least two, and sometimes three majorreactions that must proceed simultaneously and competitively at balancedrates during the process in order to provide polyurethanes with thedesired physical characteristics. One reaction is a chain-extendingisocyanate-hydroxyl reaction by which a hydroxyl-containing molecule isreacted with an isocyanate-containing molecule to form a urethane. Thisincreases the viscosity of the mixture and provides a polyurethanecontaining secondary nitrogen atom in the urethane groups. A secondreaction is a cross-linking isocyanate urethane reaction by which anisocyanate-containing molecule reacts with a urethane group containing asecondary nitrogen atom. The third reaction which may be involved is anisocyanate-water reaction by which an isocyanate-terminated molecule isextended and by which carbon dioxide is generated to blow or assist inthe blowing of the foam. This third reaction is not essential if anextraneous blowing agent, such as a halogenated, normally liquidhydrocarbon, carbon dioxide, etc., is employed, but is essential if allor even a part of the gas for foam generation is to be generated by thisin situ reaction (e.g., in the preparation of "one-shot" flexiblepolyurethane foams).

The reactions must proceed simultaneously at optimum balanced ratesrelative to each other in order to obtain a good foam structure. Ifcarbon dioxide evolution is too rapid in comparison with chainextension, the foam will collapse. If the chain extension is too rapidin comparison with carbon dioxide evolution, foam rise will berestricted, resulting in a high density foam with a high percentage ofpoorly defined cells. The foam will not be stable in the absence ofadequate crosslinking.

It has long been known that tertiary amines are effective for catalyzingthe second crosslinking reaction. However, many amines of this classhave a strong amine odor which is carried over to the polyurethane foam.

In still other cases, some tertiary amines impart a color to the productfoam known as "pinking."

In addition to problems of odor and pinking, other tertiary aminessuffer still further deficiences. For example, in some instances thecompounds are relatively high in volatility leading to obvious safetyproblems. In addition, some catalysts of this type do not providesufficient delay in foaming, which delay is particularly desirable inmolding applications to allow sufficient time to situate the preform mixin the mold. Yet other catalysts, while meeting specifications in thisarea do not yield foams with a desirable tack-free time. Lastly, somecatalysts of this type are solids causing handling problems.

It would therefore be a substantial advance in the art if a new class ofamine catalysts were discovered which overcome some of the justenumerated disadvantages of the prior art.

SUMMARY OF THE INVENTION

A new class of compounds has been discovered which have been founduseful as polyurethane catalysts. These compounds have the followingstructural formula: ##STR3## where R₁ and R₂ are independently alkyl, orwhen taken together are selected from the group consisting of morpholinoand piperazino, R₃ is selected from the group consisting of --CH₂ CH₂--, --CH₂ CH₂ CH₂ -- and ##STR4## and n is a number of 1-6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The compounds here may be prepared by resort to a wide variety ofsynthetic techniques. However, preferably these compositions areprepared by providing an anhydride of the formula: ##STR5## where R₃ isas above. The anhydride compounds are in turn reacted with ##STR6##where R₁, R₂ and n are as above.

The compounds here possess a number of useful characteristics makingthem exceptionally attractive as polyurethane catalysts. For example,the just defined compounds have rapid catalytic activity in thepolyurethane foam area. In addition, the compounds here are alsorelatively non-volatile and possess little, if any odor. Also, and mostimportantly the compounds do not cause pinking so often observed whenother testing amine catalysts are employed, particularly when polyesterpolyols are used to make urethanes. The catalysts of the invention areparticularly desirable in foaming urethanes in that they provide asufficient delay in the foaming operation to aid in processing. Yet thecatalysts also give good foams with desirable tack-free times. Thisdelay time is particularly desirable in molding applications to allowsufficient time to situate the prefoam mix in the mold. Lastly, thecompounds are easily prepared as typically described above, and arerelatively inexpensive.

To prepare polyurethanes using the catalysts here, any aromaticpolyisocyanate may be used. Typical aromatic polyisocyanates includem-phenylene diisocyanate, p-phenylene diioscyanate, polymethylenepolyphenylisocyanate, 2,4-toluene diisocyanate, 2,6-tolylenediisocyanate, dianisidine diisocyanate, bitolylene diisocyanate,naphthalene-1,4-diisocyanate, diphenylene-4,4'-diisocyanate,aliphatic-aromatic diisocyanates, such as xylylene-1,4-diisocyanate,xylylene-1,4-diisocyanate, xylylene-1,3-diisocyanate,bis(4-isocyanatophenyl) methane, bis(3-methyl-4-isocyanatophenyl)methane, and 4,4'-diphenylpropane diisocyanate.

Greatly preferred aromatic polyisocyanates used in the practice of theinvention are 2,4- and 2,6-toluene diisocyanates and methylene-bridgedpolyphenyl polyisocyanate mixtures which have a functionality of fromabout 2 to about 4. These latter isocyanate compounds are generallyproduced by the phosgenation of corresponding methylene bridgedpolyphenyl polyamines, which are conventionally produced by the reactionof formaldehyde and primary aromatic amines, such as aniline, in thepresence of hydrochloric acid and/or other acidic catalysts. Knownprocesses for preparing polyamines and corresponding methylene-bridgedpolyphenyl polyisocyanates therefrom are described in the literature andin many patents, for example, U.S. Pat. Nos. 2,683,730; 2,950,263;3,012,008; 3,344,162; and 3,362,979.

Most preferred methylene-bridged polyphenyl polyisocyanate mixtures usedhere contain about 20 to about 100 weight percent methylenediphenyldiisocyanate isomers, with the remainder being polymethylenepolyphenyl diisocyanates having higher functionalities and highermolecular weights. Typical of these are polyphenyl polyisocyanatemixtures containing about 20 to 100 weight percent methylenediphenyldiisocyanate isomers, of which 20 to about 95 weight percentthereof is the 4,4'-isomer with the remainder being polymethylenepolyphenyl polyisocyanates of higher molecular weight and functionalitythat have an average functionality of from about 2.1 to about 3.5. Theseisocyanate mixtures are known commercially available materials and canbe prepared by the process described in U.S. Pat. No. 3,362,979, issuedJan. 9, 1968 to Floyd E. Bentley.

The hydroxyl-containing polyol component which reacts with theisocyanate may suitably be a polyester polyol or a polyether polyolhaving a hydroxyl number ranging from about 700 to about 25, or lower.When it is desired to provide a flexible foam, the hydroxyl number ispreferably in the range from about 25 to 60. For rigid foams, thehydroxyl number is preferably in the range from 350 to 700. Semi-rigidfoams of a desired flexibility are provided when the hydroxyl number isintermediate to the ranges just given.

When the polyol is a polyester, it is preferable to use as thepolyester, a resin having a relatively high hydroxyl value and arelatively low acid value made from the reaction of a polycarboxylicacid with a polyhydric alcohol. The acid component of the polyester ispreferably of the dibasic or polybasic type and is usually free ofreactive unsaturation, such as ethylenic groups or acetylenic groups.The unsaturation, such as occurs in the rings of such aromatic acids asphthalic acid, terephthalic acid, isophthalic acid, or the like, isnon-ethyleneic and non-reactive. Thus, aromatic acids may be employedfor the acid component. Aliphatic acids, such as succinic acid, adipicacid, sebacic acid, azelaic acid, etc., may also be employed. Thealcohol component for the polyester should preferably contain aplurality of hydroxyl groups and is preferably an aliphatic alcohol,such as ethylene glycol, glycerol, pentaerthyritol, trimethylolethane,trimethylolpropane, mannitol, sorbitol, or methyl glucoside. Mixtures oftwo or more of the above identified alcohols may be employed also ifdesired. When a flexible urethane foam is desired, the polyol shouldpreferably have an average functionality of from about 2 to about 4 anda molecular weight of from about 2,000 to about 4,000. For rigid foams,the functionality of the polyol component is preferably from about 4 toabout 7.

When the hydroxyl-containing component is a polyether polyol for use inflexible polyurethane foam, the polyol may be an alkylene oxide adductof a polyhydric alcohol with a functionality of from about 2 to about 4.The alkylene oxide may suitably be ethylene oxide, propylene oxide, or1,2-butylene oxide, or a mixture of some or all of these. The polyolwill suitably have a molecular weight within the range of from about2,000 to about 7,000. For flexible polyether polyurethane foams, thealkylene oxide is preferably propylene oxide or a mixture of propyleneoxide and ethylene oxide.

For rigid polyether polyurethane foams, the polyol should have afunctionality of from about 4 to about 7 and a molecular weight of fromabout 300 to about 1,200. Polyols for rigid polyether polyurethane foamsmay be made in various ways including the addition of an alkylene oxideas above to a polyhydric alcohol with a functionality of from 4 to 7.These polyols may also be, for example, Mannich condensation products ofa phenol, an alkanolamine, and formaldehyde, which Mannich condensationproduct is then reacted with an alkylene oxide (See U.S. Pat. No.3,297,597).

The amount of hydroxyl-containing polyol compound to be used relative tothe isocyanate compound in both polyester and polyether foams normallyshould be such that the isocyanate groups are present in at least anequivalent amount, and preferably, in slight excess, compared with thefree hydroxyl groups. Preferably, the ingredients will be proportionedso as to provide from about 1.05 to about 1.5 mol equivalents ofisocyanate groups per mol equivalent of hydroxyl groups. However, forcertain shock absorbing foams we have found that by using the catalystsof our invention the mol equivalents of isocyanate to hydroxyl groupscan be as low as 0.4.

When water is used, the amount of water, based on the hydroxyl compound,is suitably within the range of about 0.05 mol per mol equivalent ofhydroxy compound.

It is within the scope of the present invention to utilize anextraneously added inert blowing agent such as a gas or gas-producingmaterial. For example, halogenated low-boiling hydrocarbons, such astrichloromonofluoromethane and methylene chloride, carbon dioxide,nitrogen, etc., may be used. The inert blowing agent reduces the amountof excess isocyanate and water that is required in preparing flexibleurethane foam. For a rigid foam, it is preferable to avoid the use ofwater and to use exclusively the extraneous blowing agent. Selection ofthe proper blowing agent is well within the knowledge of those skilledin the art. See for example U.S. Pat. No. 3,072,082.

The catalysts discovered here which are useful in the preparation ofrigid or flexible polyester or polyether polyurethane foams, based onthe combined weight of the hydroxyl-containing compound andpolyisocyanate, are employed in an amount of from about 0.05 to about4.0 weight percent. More often that the amount of catalyst used in0.1-1.0 weight percent. Most preferably, the catalysts here are employedto mold flexible polyester or polyether polyurethane foams.

The catalysts of this invention may be used either alone or in a mixturewith one or more other catalysts such as other tertiary amines or withan organic tin compound or other polyurethane catalysts. The organic tincompound, particularly useful in making flexible foams may suitably be astannous or stannic compound, such as a stannous salt of a carboxylicacid, a trialkyltin oxide, a dialkyltin dihalide, a dialkyltin oxide,etc., wherein the organic groups of the organic portion of the tincompound are hydrocarbon groups containing from 1 to 8 carbon atoms. Forexample, dibutyltin dilaurate, dibutyltin diacetate, diethyltindiacetate, dihexyltin diacetate, di-2-ethylhexyltin oxide, dioctyltindioxide, stannous octoate, stannous oleate, etc., or a mixture thereof,may be used.

Such other tertiary amines include trialkylamines (e.g., trimethylamine,triethylamine), heterocyclic amines, such as N-alkylmorpholines (e.g.,N-methylmorpholine, N-ethylmorpholine, etc.), 1,4-dimethylpiperazine,triethylenediamine, etc., aliphatic polyamines, such asN,N,N'N'-tetramethyl-1,3-butanediamine.

Conventional formulation ingredients are also employed, such as, forexample, foam stablizers also known as silicone oils or emulsifiers. Thefoam stabilizer may be an organic silane or siloxane. For example,compounds may be used having the formula:

    RSi[O--(R.sub.2 SiO).sub.n -(oxyalkylene).sub.m R].sub.3

wherein R is an alkyl group containing from 1 to 4 carbon atoms; n is aninteger of from 4 to 8; m is an integer of 20 to 40; and the oxyalkylenegroups are derived from propylene oxide and ethylene oxide. See, forexample, U.S. Pat. No. 3,194,773.

In preparing a flexible foam, the ingredients may be simultaneously,intimately mixed with each other by the so-called "one-shot" method toprovide a foam by a one-step process. In this instance, water shouldcomprise at least a part (e.g., 10% to 100%) of the blowing agent. Theforegoing methods are known to those skilled in the art, as evidenced bythe following publication: duPont Foam Bulletin, "Evaluation of SomePolyols in One-Shot Resilient Foams," Mar. 22, 1960.

When it is desired to prepare rigid foams, the "one-shot" method or theso-called "quasi-prepolymer method" is employed, wherein thehydroxyl-containing component preferably contains from about 4 to 7reactive hydroxyl groups, on the average, per molecule.

In accordance with the "quasi-prepolymer method," a portion of thehydroxyl-containing component is reacted in the absence of a catalystwith the polyisocyanate component in proportions so as to provide fromabout 20 percent to about 40 percent of free isocyanato groups in thereaction product, based on the polyol. To prepare a foam, the remainingportion of the polyol is added and the two components are allowed toreact in the presence of catalytic systems such as those discussed aboveand other appropriate additives, such as blowing agents, foamstabilizing agents, fire retardants, etc. The blowing agent (e.g., ahalogenated lower aliphatic hydrocarbon), the foam-stabilizing agent,the fire retardant, etc., may be added to either the prepolymer orremaining polyol, or both, prior to the mixing of the component, wherebyat the end of the reaction a rigid polyurethane foam is provided.

Urethane elastomers and coatings may be prepared also by knowntechniques in accordance with the present invention wherein a tertiaryamine of this invention is used as a catalyst. See, for example, duPontBulletin PB-2, by Remington and Lorenz, entitled "The Chemistry ofUrethane Coatings.

The invention will be illustrated further with respect to the followingspecific examples, which are given by way of illustration and not aslimitations on the scope of this invention.

EXAMPLES I-III

Typical catalysts of the invention were prepared and then utilized inmaking flexible polyurethane foam based on polyester polyols using thefollowing formulations:

    ______________________________________                                                       I       II      III                                            ______________________________________                                        FOMREZ® 50.sup.1                                                                           200.      200.    200.                                       Silicone L-532.sup.2                                                                           2.0       2.0     2.0                                        ARMEEN® DM-16D.sup.3                                                                       0.2       0.2     0.2                                        Water            7.2       7.2     7.2                                        N-(3-dimethylaminopropyl)                                                      phthalimide, 50% in                                                           dipropylene glycol                                                                            4.0       --      --                                         N-(3-dimethylaminopropyl)                                                      succinimide     --        1.9     --                                         N-(3-dimethylaminopropyl)                                                      glutarimide, 50% in                                                           dipropylene glycol                                                                            --        --      4.0                                        Toluene diisocyanate                                                                           89        86.6    89                                         Cream time (seconds)                                                                           15        12      14                                         Rise time (seconds)                                                                            100       80      78                                         ______________________________________                                         .sup.1 A product of Witco Chemical Corp., polyester made from adipic acid     and diethylene glycol approximately 2000 molecular weight.                    .sup.2 A silicone product of Union Carbide Corp.                              .sup.3 A product of Armak Chemical, palmityl dimethylamine.              

It should be noted that the catalysts of the invention have been seen tobe more efficient than N-ethylmorpholine, a typical commercial tertiaryamine catalyst, with only about 1/2 as much catalyst of the inventionneeded for comparable results. In addition, all the foams produced werewhite in color with no pink hue.

EXAMPLES IV-V

These examples show the catalysts here can also be used in makingflexible foams based on polyether polyols, as exemplified by thefollowing formulations:

    ______________________________________                                                           IV    V                                                    ______________________________________                                        THANOL® F-3016.sup.1                                                                           120.    120.                                             Silicone L-520.sup.2 1.2     1.2                                              Water                4.8     4.8                                              M&T's T-10.sup.3     0.48    0.48                                             N-(3-dimethylaminopropyl)                                                      phthalimide, 50% in dipropylene                                               glycol              0.5     --                                               N-(3-dimethylaminopropyl)                                                      succinimide         --      0.25                                             Toluene diisocyanate 62      62                                               Cream time (seconds) 15      13                                               Rise time (seconds)  113     107                                              ______________________________________                                         .sup.1 A product of Jefferson Chemical Co., a glycerine based polyether       polyol of 3000 molecular weight.                                              .sup.2 A silicone product of Union Carbide Corp.                              .sup.3 50% stannous octoate in dioctylphthalate, M&T Chemicals, Inc.     

EXAMPLE VI

Here a rigid foam was prepared. A faster reaction profile could beobtained with about half as much catalyst of the invention asN-ethylmorpholine.

    ______________________________________                                                           VI    VIa                                                  ______________________________________                                        THANOL AS-700.sup.1  232.5   226.8                                            DC-193.sup.2         0.5     0.5                                              Fluorocarbon R11B.sup.3                                                                            80.5    80.5                                             N-ethylmorpholine    --      24                                               N-(3-dimethylaminopropyl)                                                      succinimide         12.     --                                               Mondur MR.sup.4      271.5   265.2                                            Cream time           42      64                                               Rise time            230     500                                              Tack free time       160     360                                              ______________________________________                                         .sup.1 A product of Jefferson Chemical Co., Inc. propoxylated sorbitol,       molecular weight about 700                                                    .sup.2 A silicone surfactant available from                                   .sup.3 Trichlorofluoromethane                                                 .sup.4 A polymeric isocyanate available from Mobay Chemical Co.          

I claim:
 1. A method for producing a polyurethane which comprisesreacting an organic polyisocyanate with an organic polyester polyol orpolyether polyol in the presence of a catalytic amount of a compoundhaving the structural formula: ##STR7## where R₁ and R₂ areindependently alkyl, or when taken together are selected from the groupconsisting of morpholino and piperazino, R₃ is selected from the groupconsisting of --CH₂ CH₂ --, --CH₂ CH₂ CH₂ -- and ##STR8## and n is anumber of 1-6.
 2. The method of claim 1 where R₁ and R₂ are methyl. 3.The method of claim 2 where n is
 3. 4. The method of claim 1 wherein aflexible polyether polyurethane foam is provided which comprisesreacting in the presence of a blowing agent said organic polyisocyanatewith a polyether polyol formed by the addition of a polyhydric alcoholhaving a functionality of from 2 to about 4 with an alkylene oxide of 2to 4 carbon atoms in the presence of said catalyst, said organicpolyisocyanate being employed in an amount sufficient to provide 0.4 to1.5 mol equivalents of isocyanate groups per mol equivalent of hydroxylgroups, said polyether polyol having a molecular weight within the rangeof about 200-700.
 5. The method of claim 1 wherein a flexible polyesterpolyurethane foam is prepared which comprises reacting in the presenceof a blowing agent, toluene diisocyanate with a hydroxyl terminatedcondensation product of a polycarboxylic acid and a polyhydric alcoholin the presence of said catalyst, said toluene diisocyanate beingemployed in an amount sufficient to provide 1.0 to 1.5 mol equivalentsof isocyanate groups per mol equivalent of hydroxyl groups, saidcondensation product having a functionality of from about 2 to about 4,and a molecular weight from about 2,000 to about 4,000 and a hydroxylnumber ranging from about 25 to about 60.